Method and device for the separation of dust particles

ABSTRACT

A device ( 16 ) for separating particles (MP) from a flue gas flow (F) has a horizontal flue gas duct ( 18 ), through which the flue gas flow (F) is passed substantially horizontally from a first position (P 1 ) to a second position (P 2 ). In the first position (P 1 ), the device ( 16 ) has a baffle arrangement ( 32 ), which comprises at least one plate ( 34, 36, 38 ) which is arranged in the flue gas duct ( 18 ) and which is inclined so as to deflect particles (MP) down to the lower portion ( 42 ) of the horizontal flue gas duct ( 18 ). In the second position (P 2 ), the device ( 16 ) has a collecting means ( 40 ), which is arranged in the lower portion ( 42 ) of the flue gas duct ( 18 ) to collect the particles (MP) which have been deflected downwards by the plate ( 34, 36, 38 ) to the lower portion ( 42 ) of the flue gas duct ( 18 ).

FIELD OF THE INVENTION

The present invention relates to a method for separating particles froma flue gas flow which is passed substantially horizontally in a flue gasduct from a first position to a second position.

The present invention also relates to a device for separating particlesfrom a flue gas flow, which device has a horizontal flue gas duct,through which flue gas is passed substantially horizontally from a firstposition to a second position.

BACKGROUND ART

Flue gas cleaning plants for, inter alia, coal-fired and oil-fired powerstations, waste incineration plants etc. often have what is referred toas an SCR reactor. An SCR (Selective Catalytic Reduction) reactorinvolves a reactor in which a catalytically induced, selective reductionof nitrogen oxides occurs. The SCR reactor has a catalyst, which oftenis configured as a honeycomb structure or as a number of closely spacedplates to provide a maximum reactive surface. A drawback in many SCRreactors is that particulate dust, which is formed in the burning of,for instance, coal, oil or waste, gets stuck in the SCR reactor andclogs it.

U.S. Pat. No. 5,687,656 in the name of Kaneko et al discloses a methodof reducing the amount of dust that reaches and clogs an SCR reactor. Inthe method according to U.S. Pat. No. 5,687,656, a flue gas is firstpassed in a horizontal flue gas duct, then in a vertical flue gas ductand subsequently through a porous plate, which has a pore size smallerthan the particles that are to be separated.

The method according to U.S. Pat. No. 5,687,656 may cause a reduction ofthe amount of dust that reaches the SCR reactor. A problem with thisporous plate, however, is the risk of it being clogged by dustparticles. Such clogging causes an increase in pressure drop and, thus,increased operating expenses.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method of separatingparticles from a flue gas, which method wholly or partly eliminates theabove drawbacks.

This object is achieved by a method of separating particles from a fluegas flow, which is passed substantially horizontally in a flue gas ductfrom a first position to a second position, said method beingcharacterised in that in the first position the particles are subjectedto deflection downwards to the lower portion of the flue gas duct, andthat in said second position the particles are collected at the lowerportion of the flue gas duct.

An advantage of this method is that the deflection, which can beprovided by simple means and with a low pressure drop, in the firstposition surprisingly provides a considerable up-concentration ofparticles at the lower portion of the duct. In particular largeparticles, such as particles larger than about 1 mm, will be heavilydeflected and in such a manner that they are not redispersed in the fluegas flow. The collection in the second position occurs at the lowerportion of the flue gas duct, i.e. precisely where the particles havebeen up-concentrated. This means that the collection does not have tooccur from the entire flue gas flow but only from that partial flow ofthe flue gas flow in which the particles have been up-concentrated.

In a preferred embodiment, the particles are deflected downwards at anangle of 40-70° to the horizontal plane. An angle of 40-70° has beenfound to give the optimum deflection of the particles. At an angle whichis smaller than about 40° the deflection will not be sufficiently greatand the particles will thus not be up-concentrated at the lower portionof the flue gas duct but will be redispersed in the flue gas. At anangle which is greater than about 70°, the pressure drop will increase.There is also a risk that the deflection will be so great that theparticles bounce against the bottom of the flue gas duct and areredispersed in the flue gas flow.

In a preferred method, the flue gas flow is in the second positiondivided into a first partial flow, which contains the deflectedparticles and which is deflected from the lower portion of the flue gasduct and is passed downwards into a collecting chamber, and a secondpartial flow. The first partial flow provides a simple and reliable wayof removing by few movable parts the particles that have beenup-concentrated from the flue gas flow at the lower portion of the fluegas duct.

Preferably, the first partial flow is made to undergo a sharp turn inthe collecting chamber, the particles being thrown out of the firstpartial flow and separated in the collecting chamber. To remove theparticles by centrifugal force from the first partial flow has theadvantage that a net, porous plates and other means which can easily beclogged are not necessary for the separation of the particles. Thisresults in great reliability in operation.

In a preferred method, the velocity of the flue gas flow is decreased bya factor which is 1.2 to 2.5, while the flue gas flow is passed from thefirst position to the second position. An advantage of this is that theparticles which in the first position have been deflected to the lowerportion of the flue gas duct will not be redispersed in the flue gasflow as this is passed from the first position to the second position.On the contrary, the decreasing gas velocity will result in furtherup-concentration of the particles at the lower portion of the duct owingto what can be designated as a settling effect.

A further object of the present invention is to provide a device foreffective separation of particles from a flue gas, in which device theabove-mentioned drawbacks are wholly or partly eliminated.

This object is achieved by a device which is of the type defined by wayof introduction and characterised in that the device in the firstposition has a baffle arrangement, which comprises at least one platewhich is arranged in the flue gas duct and which is inclined so as todeflect particles down to the lower portion of the horizontal flue gasduct, and that the device in the second position has a collecting means,which is arranged in the lower portion of the flue gas duct to collectthe particles which have been deflected downwards by the plate to thelower portion of the flue gas duct. An advantage of this device is thatit provides effective separation of the particles that may be expectedto clog an SCR reactor without causing a high pressure drop or a risk ofthe device being clogged.

In a preferred embodiment, said at least one plate makes an angle of40-70° to the horizontal plane. A plate with such an angle has beenfound to imply that particles effectively bounce down to the lowerportion of the flue gas duct.

Preferably the collecting means has a deflecting wall, which opposite tothe flow direction of the flue gas flow extends into the flue gas ductin the lower portion thereof and which above the bottom of the flue gasduct is terminated by a deflecting line, and which wall is arranged todeflect from the flue gas flow a partial flow, which contains thedeflected particles and is arranged to be passed into a collectingchamber included in the collecting means. The deflecting wall results ineffective collection of the particles that have been deflected in thefirst position without causing a high pressure drop or a risk ofclogging.

Suitably the collecting chamber has a collecting wall, which extendsfrom the collecting chamber portion which is positioned closest to thefirst position, to the deflecting wall at a level below the deflectingline. An advantage of the collecting wall is that it improves theremoval of particles from the partial flow and reduces the risk thatalready separated particles in the collecting chamber should beentrained by the flue gas flow.

The baffle arrangement suitably comprises at least three inclinedplates. With at least three inclined plates, a baffle arrangement can beprovided, which has a low pressure drop and which causes a small riskthat particles pass the baffle arrangement without bouncing on a plateand being deflected to the lower portion of the flue gas duct. Dependingon the height of the flue gas duct in the vertical direction, it mayoften be convenient to use even more plates, such as 4, 5 or 6 plates oreven more.

In a preferred embodiment, the cross-sectional area of the horizontalflue gas duct is 1.2-2.5 times greater in the second position than inthe first position. This relationship between the cross-sectional areasmeans that the velocity of the flue gas is reduced, which improves theseparation of particles in the second position. The cross-sectional areaof the flue gas duct in the second position should be at least 1.2 timesthe cross-sectional area of the flue gas duct in the first position soas to prevent the particles deflected to the lower portion of the fluegas duct from being redispersed in the flue gas. In an area relationshipwhich is greater than 2.5, a separation also of very small particles isprovided, which still do not cause a risk of clogging of, for instance,an SCR reactor but are rather separated in a dust separator arrangedafter the SCR reactor.

Preferably, the length of the flue gas duct from the first position tothe second position is at least twice its characteristic cross-sectionaldimension, such as a diameter or a height, in the first position. Such alength gives also the particles, which are positioned close to the upperportion of the flue gas duct as they are being deflected by the bafflearrangement, enough time to move down to the lower portion of the fluegas duct so as to be separated in the collecting means. If thecross-sectional area of the flue gas duct increases from the firstposition to the second position, the above-mentioned length is alsonecessary for the flue gases to have time to spread in the increasedcross-sectional area and cause the reduction of velocity requested insuch a case.

Additional features and advantages of the present invention will beevident from the following description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described by way of a number ofembodiments and with reference to the accompanying drawings.

FIG. 1 is a schematic side view and shows a power station which isequipped with a device according to the invention.

FIG. 2 is a side view and shows the device according to the invention inmore detail.

FIG. 3 is a side view and shows how particles are deflected andcollected in the device shown in FIG. 2.

FIG. 4 is a side view and shows how particles are deflected andcollected in an alternative embodiment of a device according to theinvention.

FIG. 5 is a side view and shows a baffle arrangement according to analternative embodiment.

FIG. 6 is a side view and shows a baffle arrangement according toanother alternative embodiment.

FIG. 7 is a side view and shows yet another alternative embodiment ofthe present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a power station 1. The power station 1 has a boiler 2, inwhich a fuel, such as coal, oil or waste, is burnt by being contactedwith supplied air. The flue gases F and the particles formed in theburning are passed through a duct 4 to a flue gas cooler, also referredto as an economiser, 6. In the flue gas cooler 6 heat is extracted fromthe flue gases as they are being passed vertically downwards through apackage of tubes 8 and there being brought into indirect contact withthe feed water of the boiler 2. The flue gas cooler 6 has in its lowerportion 10 a dust hopper 12 which collects some coarse particles. Adischarge device 14 is used to remove such collected coarse particles.In the lower portion 10 of the flue gas cooler 6, the flue gases changefrom a vertical direction of flow to a horizontal direction of flow andare passed into a device 16 according to the invention.

The device 16 has a horizontal flue gas duct 18, which passes the fluegases in a substantially horizontal direction from a first position P1,which is located in the connection of the flue gas duct 18 to the lowerportion 10 of the flue gas cooler 6, to a second position P2 in whichthe direction of the flue gases is changed to vertical and the fluegases are passed vertically upwards in a vertical flue gas duct 20. Theflue gases are then turned through 180° and passed into an SCR reactor22, which is intended for selective catalytic reduction of nitrogenoxides. In the shown embodiment the SCR reactor 22 has three catalystlayers 24, 26, 28 which contain a catalyst formed to a honeycombstructure. The flue gases pass through a number of narrow ducts, whichtypically have openings which are 4 by 4 mm in cross-section, in thecatalyst while the nitrogen oxide content of the flue gases is reduced.The flue gases leave the SCR reactor 22 through a gas duct 30 and arethen further cleaned, for instance, in an electrostatic precipitator anda flue gas desulphurisation plant, which are not shown in FIG. 1, so asthen to be released into the atmosphere.

The particles collected in the dust hopper 12 are only the coarsestparticles. The flue gas leaving the lower portion 10 of the flue gascooler 6 will therefore contain a large number of particles that havesuch a size that, if they reached the catalyst layers 24, 26, 28, theywould clog the narrow ducts in the honeycomb structure and cause anincreased pressure drop and impaired reduction of nitrogen oxides. Forthe purpose of avoiding such problems, the device 16 has been providedwith a baffle arrangement 32, which has three inclined plates 34, 36,38, in the first position P1, and a collecting means 40 in the secondposition P2.

FIG. 2 shows the device 16 in more detail. The baffle arrangement 32arranged in the first position P1 has, as mentioned above, three plates34, 36, 38. These plates, which are placed vertically one above theother, are inclined so as to deflect flue gases, in the form of a fluegas flow F, and above all particles by a “bouncing effect” down to thelower portion 42 of the flue gas duct 18. As is evident from FIG. 2, theplates 34, 36, 38 are inclined at an angle α of about 45° to thehorizontal plane seen in the flow direction of the flue gas flow F andare thus, seen in the flow direction of the flue gas flow, directeddownwards. As shown in FIG. 2, the flue gas duct 18 has an upper wall 44which, seen in the flow direction of the flue gas flow, is inclinedupwards at an angle β to the horizontal plane. The angle β is about 10°.This angle implies that the cross-sectional area A2 of the flue gas duct18 in the second position P2 will be about 1.5 times the cross-sectionalarea A1 in the first position P1. The flue gas duct 18 has a length Lwhich is about 3.5 times the dimension D of the flue gas duct 18, whichdimension can be a height or a diameter according to the shape of theduct, in the first position P1.

The collecting means 40, which is arranged in the lower portion 42 ofthe flue gas duct 18, is located in the second position P2. Thecollecting means 40 has a collecting chamber 46 which is arranged underthe flue gas duct 18 and is in the shape of an equilateral triangle withits tip pointed downwards. The walls of the collecting chamber 46 makean angle γ of about 60° to the horizontal plane. A discharge device 48,which may comprise a fluidised transport system, is used for periodicemptying of the collecting chamber 46. The collecting means 40 furtherhas a deflecting wall 50, which extends in a direction opposite to theflow direction of the flue gas flow into the flue gas duct 18 in thelower portion 42 thereof. As shown in FIG. 2, the wall 50 starts fromthe end of the collecting chamber 46, which is the far end seen in theflue gas flow direction, and extends obliquely upwards into the flue gasduct 18. The deflecting wall 50 makes an angle δ of about 60° to thehorizontal plane and is terminated by a deflecting line 52, whichextends transversely to the flue gas duct 18 in the horizontaldirection. From the deflecting line 52 extends in the flue gas flowdirection a rear wall 54 included in the vertical flue gas duct 20.

The collecting chamber 46 further has a collecting wall 56, whichextends from the wall 58 of the collecting chamber 46 which is closestto the first position P1 to the deflecting wall 50 and at a level in thevertical direction which is located below the level, in the verticaldirection, of the deflecting line 52, which in turn is located above thebottom 60 of the flue gas duct 18.

FIG. 3 shows how flue gases F and medium-coarse Particles MP can beexpected to behave in the device 16 in operation. Medium-coarseparticles here refer to particles of a size greater than about 1 mm butsmaller than about 10 mm, which is the particle sizes that may beexpected to cause maximum problems with clogging in the catalyst layers24, 26, 28. Coarse particles, which refer to particles of a size greaterthan about 10 mm, will frequently be separated in the dust hopper 12 ofthe flue gas cooler 6, but in cases where this does not occur, alsothese particles will be separated in the device 16. Fine particles,which refer to particles of a size smaller than 1 mm, will be separatedin the device 16 to a limited extent only. As mentioned above, the fluegas flow F will, when leaving the lower portion 10 of the flue gascooler 6, be reversed to a substantially horizontal flow direction. Asthe flue gas flow F reaches the baffle arrangement 32 arranged in thefirst position P1, the flue gas flow F will be deflected downwards tothe lower portion 42 of the flue gas duct 18. The velocity of the fluegas flow F in the first position P1 is about 20 m/s. When the flue gasflow F is passed to the second position P2, the effects of thedeflection will fade and the flue gas flow F in the second position P2will have a fairly uniform gas velocity profile. Since thecross-sectional area A2 in the second position P2 is greater than thecross-sectional area A1 in the first position P1, the velocity of theflue gas flow F will gradually decrease to become about 13 m/s in thesecond position P2.

The medium-coarse particles MP will, as is evident from FIG. 3, bumpinto the plates 34, 36, 38 and bounce downwards to the lower portion 42of the flue gas duct 18. FIG. 3 shows typical patterns of movements forthese particles MP by dashed lines. As indicated in FIG. 3, someparticles MP can, when leaving the lower portion 10 of the flue gascooler 6, have a movement directed obliquely upwards, but also theseparticles MP are deflected downwards by the plates 34, 36, 38. Afterhaving thus bounced down to the lower portion 42 of the flue gas duct18, the medium-coarse particles MP will not be redispersed in the fluegas flow F but continue to move along the bottom 60 of the duct 18. Thebaffle arrangement 32 will have an equalising effect on the velocityprofile of the flue gas flow F in the flue gas duct 18 and reduce theformation of eddies which could whirl up the particles MP from the lowerportion 42. The fact that the velocity of the flue gas flow F decreasesfrom the first position P1 to the second position P2 further reduces thetendency of the flue gas flow F to get hold of the medium-coarseparticles MP again and entrain them. On the contrary, a settling effectis achieved owing to this reduction of velocity, where the medium-coarseparticles MP are moved closer and closer to the bottom 60 of the duct18. In the second position P2 the deflecting line 52, in which astagnation point is formed, will deflect a first partial flow FP, whichis passed downwards by the deflecting wall 50 into the collectingchamber 46. The deflecting line 52 should be placed at such a levelabove the bottom 60 and the deflecting wall 50 should have such an angleδ to the horizontal plane that the first partial flow FP obtains a gasvelocity of maximum about 5-6 m/s in a standing eddy which is formed inthe collecting chamber 46. The rest of the flue gas flow is deflected asa second partial flow FF by the wall 54 upwards and into the verticalflue gas duct 20. The deflected first partial flow FP will entrain themedium-coarse particles MP and press them down into the collectingchamber 46. In the collecting chamber 46 the partial flow FP is causedto make a sharp turn, thus making the medium-coarse particles MP beingpressed by centrifugal force out against the walls 58 of the chamber 46and thus being separated. The collecting wall 56 will contribute to thesharp turn that the partial flow FP is forced to make and furtherincrease the amount of particles MP which is removed from the partialflow FP. Moreover the collecting wall 56 will reduce the risk thatparticles can be entrained from the collecting chamber 46 andredispersed in the flue gas. As is evident from FIG. 3, the partial flowFP will after the sharp turn past the collecting wall 56 again be mixedwith the flue gas flow. According to the design of the collecting means40, the partial flow FP can form a more or less stable standing eddy inthe collecting chamber 46 with a greater or smaller gas exchange withthe main flue gas flow. Irrespective of the gas exchange, the partialflow FP will, however, entrain the particles MP down into the collectingchamber 46.

FIG. 4 shows an alternative embodiment of the present invention in theform of a device 116. The device 116 has a horizontal flue gas duct 118,which passes a flue gas flow F in a substantially horizontal directionfrom a first position P1, which is positioned in the connection of theflue gas duct 118 to a flue gas cooler (not shown in FIG. 4), to asecond position P2 after which the flue gas flow F is passed onhorizontally in a horizontal flue gas duct 120 to an SCR reactor notshown in FIG. 4. The device 116 further has in the first position P1 abaffle arrangement 132, which has inclined plates 134, 136, 138 and isof the same type as the baffle arrangement 32 shown above. In the bafflearrangement 132, the medium-coarse particles MP will be deflected,“bounce”, down to the lower portion 142 of the flue gas duct 118. In thesecond position P2, the device 116 has a collecting means 140, which hasa collecting chamber 146 which is of the same type as the chamber 46shown in FIG. 2. The collecting means 140 further has a horizontaldeflecting wall 150 which extends into the flue gas duct 118 in thedirection opposite to the flow direction of the flue gas flow F and isterminated by a deflecting line 152, which is located above the bottom160 of the flue gas duct 118. In the collecting chamber 146 a collectingwall 156 is mounted, which is of the same type as the collecting wall 56and extends at a level below the deflecting wall 150. As shown in FIG.4, the deflecting wall 150, which thus makes an angle of 0° to thehorizontal plane, will at the deflecting line 152 deflect a partial flowFP which is passed down into the chamber 146 and there makes a sharpturn while the medium-coarse particles MP are being separated. The restof the flue gas flow, symbolised by a partial flow FF, continues to thehorizontal flue gas duct 120. It will be appreciated that the partialflow FF will also contain flue gases leaving the chamber 146, whichmeans that the partial flow FF will be of the same size as the flue gasflow F which is supplied to the flue gas duct 118. The deflected partialflow FP in the chamber 146 forms a standing eddy with more or lessexchange with the rest of the flue gas flow. The flue gas duct 118 has,like the flue gas duct 18 shown in FIG. 2, an upper wall 144 which, seenin the flow direction of the flue gas flow, is inclined upwards to thehorizontal plane. Thus, the velocity of the flue gas flow will be lowerin the second position P2 than in the first position P1, which reducesthe risk that the particles MP which have bounced down to the lowerportion 142 will again be dispersed in the flue gas. In an alternativeembodiment, the deflecting wall 150 can be provided with a hinge at itspoint of attachment and thus be pivotable, which is indicated by dashedlines in FIG. 4, for adjustment of the angle of the wall 150 to thehorizontal plane and, thus, of a suitable first partial flow FP.

FIG. 5 shows a baffle arrangement 232 according to an alternativeembodiment. The baffle arrangement 232, which is arranged in a flue gasduct 218, which is of the same type as the flue gas duct 18 describedabove, has five inclined plates 234, 235, 236, 237, 238. These platesare placed along a line which is inclined at an angle ε of about 45° tothe horizontal plane and which line thus, seen in the flow direction ofthe flue gas flow F, is inclined upwards. Thus, the plates 234, 235,236, 237, 238 are not placed vertically one above the other. As isevident from FIG. 5, the plates 234 and 235 overlap each other, seen inthe horizontal direction, a distance O (the remaining plates overlapeach other correspondingly). This overlap O decreases the risk that aparticle, symbolised by MP, can pass the baffle arrangement 232 withoutcolliding against a plate 234, 235, 236, 237, 238, which is alsoillustrated in FIG. 5 with two typical paths of movement formedium-coarse particles MP.

FIG. 6 shows a baffle arrangement 332 according to another alternativeembodiment. The baffle arrangement 332, which is arranged in a flue gasduct 318, which is of the same type as the flue gas duct 18 describedabove, has three inclinable plates 334, 336, 338. Each plate 334, 336,338 is, which in FIG. 6 is indicated by a respective dashed plate,pivotable on an associated horizontal shaft 335, 337, 339. Thehorizontal shafts 335, 337, 339 are attached to an actuator 341 which isschematically indicated and arranged outside the flue gas duct 318 andcomprises a guide rail 343 which is connected to a motor 345. Theposition of the guide rail 343 in the vertical direction can be set bythe motor 345, and consequently the plates 334, 336, 338 can be pivotedto a desired angle α to the horizontal plane. Thus, it can be tried outby experiments what angle α gives a sufficient separation of themedium-coarse particles so as to prevent clogging of the SCR reactorwithout causing an unnecessarily high pressure drop across the bafflearrangement 332. The baffle arrangement 332 can also be configured insuch a manner that the plates can be pivoted to an angle α of 90° to thehorizontal plane, in which case the baffle arrangement 332 may alsofunction as a shut-off damper.

FIG. 7 shows a device 416 according to yet another alternativeembodiment. The device 416, which is much the same as the device 16shown in FIG. 2 and therefore will not be described in all details, isconnected after a flue gas cooler 406, which is only partly shown inFIG. 7. The flue gas cooler 406 is passed by an upwards directedvertical flue gas flow F. In the upper portion 410 of the flue gascooler 406 the flue gas flow F changes to a horizontal flow directionand flows into the device 416. The device 416 has a flue gas duct 418and, arranged therein, a baffle arrangement 432 which has three inclinedplates 434, 436, 438. As is evident from FIG. 7, medium-coarse particlesMP will bounce on the plates 434, 436, 438 and be heavily deflected downto the lower portion 442 of the duct 418. The baffle arrangement 432will also deflect the flue gas flow F and contribute to make the gasvelocity profile in the duct 418 uniform, which reduces the risk of thedeflected particles MP again being dispersed in the flue gas flow F. Thedevice 416 further has a collecting means 440, which has a deflectingwall 450. The deflecting wall 450 will, in a manner similar to thatdescribed with reference to FIG. 3, deflect a partial flow FP whichpasses the medium-coarse particles MP down into a collecting chamber446.

It will appreciated that many modifications of the embodiments describedabove can be made within the scope of the appended claims.

For instance, it will be appreciated that the separation of particlesperformed by the device can be adjusted by selecting suitable plates ofthe baffle arrangement in terms of number, size and angle of the platesto the horizontal plane, so that particles of such a size that they riskto clog the catalyst layers involved are separated to the desired extentwithout the pressure drop in the device being unnecessarily high. Theopenings in the catalyst have a size which can be designated d_(H). Arule of the thumb is that the main part of the particles having a sizeequal to or greater than 0.5*d_(H) should be separated before they reachthe catalyst. In the example described in FIG. 1, the openings aresquares with 4 mm sides, i.e. d_(H)=4 mm, which means that particleswith a size of 2 mm and larger should be separated before the catalyst.

The walls of the collecting chamber 46 need not necessarily make anangle γ of about 60° to the horizontal plane. The angle γ is selected insuch a manner that a suitable flow ratio of the partial flow FP in thecollecting chamber 46 is achieved and so that separated particles canslide down to the discharge device 48 at the bottom of the collectingchamber 46. It has been found that in many cases an angle γ of about40-70° very well satisfies these criteria.

As is evident from that stated above, the deflecting wall 50, 150 canmake different angles δ to the horizontal plane. In many cases an angleδ of about 0-70° is preferred to provide an appropriate first partialflow FP.

The velocity of the flue gas flow in the flue gas duct 18; 118 can bevaried within wide limits. However, it is especially preferred for thevelocity of the flue gas flow F in the first position P1 to be about13-25 m/s since a velocity in this range implies that the medium-coarseparticles MP effectively bump against the plates 34, 36 etc. down to thelower portion 42; 142 of the flue gas duct 18; 118.

1. A method of separating particles from a flue gas flow that flowssubstantially horizontally from a first position to a second position ina horizontally extending flue gas duct having a lower portion comprisingthe steps of: subjecting the particles to deflection in the firstposition of the horizontally extending flue gas duct downwards to thelower portion of the horizontally extending flue gas ducts, wherein theparticles are deflected downwards at an angle of 40 degrees-70 degreesto the horizontal plane of the horizontally extending flue gas duct;dividing the flue gas flow in the second position of the horizontallyextending flue gas duct into both a first partial flow containing thedeflected particles that is deflected to the lower portion of thehorizontally extending flue gas duct and flows downwardly into acollecting chamber, and a second partial flow; and collecting in thesecond position of the horizontally extending flue gas duct theparticles from the lower portion of the horizontally extending flue gasduct.
 2. The method of separating particles from a flue gas flow asclaimed in claim 1 further comprising the step of: making the firstpartial flow undergo a sharp turn in the collecting chamber such thatthe deflected particles contained in the first partial flow are thrownout of the first partial flow and are thereby separated from the firstpartial flow in the collecting chamber.
 3. A device for separatingparticles from a flue gas duct comprising: a horizontally extending fluegas duct through which the flue gas flow is made to flow substantiallyhorizontally from a first position of the horizontally extending fluegas duct to a second position of the horizontally extending flue gasduct, the horizontally extending flue gas duct having a lower portion; abaffle arrangement located at the first position of the horizontallyextending flue gas duct, the baffle arrangement including at least oneplate, the at least one plate being inclined so as to deflect particlesfrom the flue gas flow down to the lower portion of the horizontallyextending flue gas duct, wherein the at least one plate is inclined atan angle of 40 degrees-70 degrees to the horizontal plane of thehorizontally extending flue gas duct; and a collecting means located atthe second position of the horizontally extending flue gas duct forcollecting the particles at the first position of the horizontallyextending flue gas duct have been deflected by the at least one platefrom the flue gas flow downwards to the lower portion of thehorizontally extending flue gas duct, wherein the collecting meansincludes a deflecting wall that extends into the lower portion of thehorizontally extending flue gas duct opposite to the flow direction ofthe flue gas flow and above the bottom of the horizontally extendingflue gas duct and terminates in a deflecting line such that thedeflecting wall is arranged so as to deflect from the flue gas flow afirst partial flow that contains the deflected particles and that isarranged so as to flow into a collecting chamber that is included intothe collecting means.
 4. The device for separating particles from a fluegas flow as claimed in claim 3 wherein the collecting means includes acollecting wall that extends from the portion of the collecting chamberthat is positioned closest to the first position of the horizontallyextending flue gas duct at a level below the deflecting line of thedeflecting wall of the collecting means.